High temperature total consumption sample introduction system coupled to microwave plasma optical emission spectrometry (MIP-OES) for the analysis of aqueous samples

Abstract

The high temperature torch integrated sample introduction system (hTISIS) is coupled to microwave plasma optical emission spectrometry (MIP-OES) for the first time. The goal of this work is to develop an accurate analysis of digested samples under continuous sample aspiration mode by coupling the hTISIS to a MIP-OES instrument. To achieve this, different operating conditions such as, nebulization flow rate, liquid flow rate and the spray chamber temperature were optimized in terms of sensitivity, limits of quantification (LOQs) and background equivalent concentration (BECs) for the determination of Ca, Cr, Cu Fe, K, Mg, Mn, Na, Pb and Zn, and these values were compared with those reported with a conventional sample introduction system. Under optimum conditions (0.8–1 L min−1, 100 μL min−1 and 400 ᵒC, respectively), the hTISIS improved MIP-OES analytical figures of merit and shortened 4-times wash out times with respect to a conventional cyclonic spray chamber, reporting an enhancement factor in the sensitivity among 2–47 times and LOQs from 0.9 to 360 μg kg−1. Once the best operating conditions were set, the magnitude of the interference caused by 15 different acid matrices (2, 5 and 10% w/w of HNO3, H2SO4, HCl and mixtures of HNO3 with H2SO4 and HNO3 with HCl) was significantly lower for the former device. Finally, 6 different digested oily samples (used cooking oil, animal fat, corn oil and the same samples after a filtration step) were analyzed by means of an external calibration approach based on the use of multielemental standards prepared in 3% (w/w) HCl solution. The obtained results were compared against those supplied by a conventional methodology employing an inductively coupled plasma optical emission spectrometry, ICP-OES, instrument. It was clearly concluded that the hTISIS coupled to MIP-OES afforded similar concentrations as compared to the conventional methodology.